Month: June 2016

If you have an Ubuntu system with an NVida video card, and after suspending and resuming you get a login screen, but after you log in you get a black screen, and using ctrl + alt + F1 gets you a text console, your problem is probably lightlocker. I’ve seen some sites claim that the problem is fixable with sudo apt-get remove --purge nvidia-* which would be great if you didn’t want video drivers or CUDA. I’d rather hang onto my video drivers, so sudo apt-get remove light-locker makes everything better.

I recently wanted to do some computer vision stuff using OpenFace, which is a collection of face-processing computer vision algorithms and tools to use them. It uses OpenCV 3.0.something, which uses, among other things, vtk6, and friends libvtk6-dev and python-vtk6.

Normally, this wouldn’t be a problem, but I use ROS Indigo, as does the lab I work in. ROS Indigo uses some previous version of vtk, and so attempting to install OpenCV 3.0 blows away my ROS install, and makes apt freak out when I try to install it again. The actual error was something like “you have broken held packages”, only I didn’t actually have held packages OR broken packages.

Apt just gives up at this point. Aptitude, on the other hand, proposes removing the offending VTK packages and proceeding with the ROS install. Only time will tell if I’ve trashed my OpenCV install, but if I have, I can just go back to an older OpenCV version.

Given a file containing a list of songs, one per line, in the format “Artist – Song Title”, download the audio of the first youtube video link on a Google search for that song. This is quite useful if you want to the MP3 for every song you ever gave a thumbs up on Pandora. On my computer, this averages about 4 songs a minute.

The Requests API and BeautifulSoup make writing screenscrapers and automating the web really clean and easy.

The white version of the TinyRobo board that has the missing ground trace also doesn’t have a proper connection for the pullups on the I2C address lines for the motor drivers. The drivers are still there, and scanning the I2C bus with a Bus Pirate (Amazon) showed me that they were at 0x63 and 0x64 on the I2C bus, rather than where I expected them to be (at 0x66 and 0x68). The difference is consistent with a connection that should have been to Vcc being left open.

I’m not wild about the problem, but it did give me an opportunity to set up and use Pulseview/Sigrok, my cheap clone logic analyzer, and my Bus Pirate, so it’s not a total waste.

For my own future reference, as well as anyone else who’s interested, the way to set up the Bus Pirate on Ubuntu is this:

Plug it into a USB port

Open up a terminal and type screen /dev/buspirate 115200 8N1 , where /dev/buspirate is whatever device your bus pirate ended up on. Mine was /dev/ttyUSB0.

The terminal will go blank. Hit enter, and you should get the “HiZ>” Bus Pirate terminal.

The I2C bus scan is run by hitting “m” to get the menu, “4” to get I2C mode, “3” to set speed to 100kHz, and then “(1)” to run the scan macro.

The cheapo logic analyzer I got is a USBee & Saleae clone, which I got because I’m bad and should feel bad not rich. It has a switch to determine which device it claims to be. In Saleae mode, Sigrok loads an alternate firmware onto it, so I’m not really sure where that falls in the intellectual property/doing the right thing by small businesses framework, but if you can afford one, get a proper USBee or Saleae. They’re much better built (the Saleae Logics in particular are tanks) and have more and better features.

I’m doing all this stuff in Enschede, at U. Twente. I’ve been hanging out with the people in the HMI group, which “does things with stuff”. They do a lot of work with things like proxemics in interaction, socially aware robots and technology, and so forth. There’s something of a distinction here between technical stuff, which is what I do a lot of, and more abstract work with avatars and such. I’m a better fit with the RaM (Robotics and Mechatronics) group, which builds things like pipe-crawling robots and quadcopters.